Cutting edge: rapid in vivo CTL activity by polyoma virus-specific effector and memory CD8+ T cells.

For viruses that establish persistent infection, continuous immunosurveillance by effector-competent antiviral CD8(+) T cells is likely essential for limiting viral replication. Although it is well documented that virus-specific memory CD8(+) T cells synthesize cytokines after short term in vitro stimulation, there is limited evidence that these T cells exhibit cytotoxicity, the dominant antiviral effector function. Here, we show that antiviral CD8(+) T cells in mice acutely infected by polyoma virus, a persistent mouse pathogen, specifically eliminate viral peptide-pulsed donor spleen cells within minutes after adoptive transfer and do so via a perforin-dependent mechanism. Antiviral memory CD8(+) T cells were similarly capable of rapidly mobilizing potent Ag-specific cytotoxic activity in vivo. These findings strongly support the concept that a cytotoxic effector-memory CD8(+) T cell population operates in vivo to control this persistent viral infection.